As hardware processor technologies are developing, the performance of embedded systems is dramatically improved. Thus, the embedded systems can be connected to external communication devices through fixed line and mobile networks. As a general-purpose operating system such as Linux can be used in PDP and PMP devices, external programs created by users or program generators can be executed in the embedded systems. Therefore, the security of the embedded systems becomes very important.
In a general-purpose operating system such as Linux, security methods are based on a multi-user environment, such as a conventional server-client environment. In a multi-user environment, operating systems should separate user processors from system management processors in order to protect a system from users. For this purpose, the operating systems maintain a separate superuser account having most privileges required for managing the system. In a Unix type operating systems such as Linux, the superuser account is usually called root account. The root account has privileges for binding a particular port and a processor, loading a kernel module, mounting and unmounting filesystems, and various system managements.
Therefore, in conventional Linux operating systems, security methods are designed based on a user account instead of the root account. A representative example is a security kernel. The security kernel improves internal security of a kernel. That is, file access is allowed only to a user account of a user having a corresponding file, and network connection and communication between processors are allowed to a user account having corresponding privileges.
Since the embedded systems are usually operated in single user environment instead of in a multi-user environment, such as a server-client environment, one user uses the embedded systems. Thus, in the embedded system, user accounts are not needed and most processors are executed with the root account.
FIG. 1 is a block diagram illustrating an environment in which an application program is executed in an embedded system according to a conventional security method. Referring to FIG. 1, each of processors of application programs 110, 120 and 130 (hereinafter, referred to as an application program processor) is executed with the root account and can access a Linux kernel 100 without any limitation. Because the application program processors 110, 120 and 130 can exercise all of the privileges accorded to the superuser (hereinafter, referred to as superuser privileges) even when they need part of superuser privileges, or do not need superuser privileges, they can access the imbedded system unnecessarily. Therefore, it is an inefficient way and a threat to the security of the embedded system to execute an application program in the embedded system according to the conventional security method based on the multi-user environment.